The present invention relates to a high-pressure fuel pump control apparatus for an internal combustion engine mounted on automobiles, and the like, and in particular, a high-pressure fuel pump control apparatus for an internal combustion engine used for a fuel supply system of in-cylinder injection engines.
Recently, automobiles are required to reduce carbon oxide (CO), hydrocarbon (HC), nitrogen oxide (NOx) and the like, included in the emission gas substances from a viewpoint of environment conservation. As an automobile engine for reducing these substances, in-cylinder injection engines have been developed. In the in-cylinder injection engine, the fuel is injected directly through a fuel injection valve into the combustion chamber of the cylinders. By lessening particle diameter of the fuel injected through the fuel injector valve, the combustion of the injected fuel in the combustion chamber is promoted in order to reduce the emission gas substances and improve the engine output.
To decrease the particle diameter of the fuel injected from the injection valve, a means for high pressurization of the injected fuel is required, and various kinds of high-pressure fuel pumps for sending high-pressurized fuel to the solenoid valve as well as control techniques for the high-pressure fuel pump have been proposed.
For example, as a fuel pressure pump used for the in-cylinder injection engine, a high-pressure fuel pump which controls the flow rate of the high-pressure fuel supplied in response to the injected fuel quantity of the fuel injection valve by actuating closing timing of the solenoid valve mounted as a pump suction valve is well-known (For example, Japanese laid-open patent publication 2000-8997). The solenoid valve used for the high-pressure pump includes two types of solenoid valves, a normal open type, which is closed by the power energization, and a normal close type, which is opened by the power energization.
In a high-pressure pump which provides a normal close type solenoid valve as a suction valve, when the power energization to the solenoid valve is carried out in the pump compression stoke, the solenoid valve is opened to prevent discharging fuel, on the other hand, when the power energization to the solenoid valve is not carried out under the pump compression stoke, the solenoid valve is closed to perform fuel discharging. Thereby, the full discharge is realized by non-power energization.
As the high-pressure fuel pump control apparatus, the following type has been proposed. Rising of the fuel pressure can be promoted from the engine starting, by outputting driving signals to the high-pressure fuel pump at least more than two times, from a signal detection timing of the crank angle sensor of the engine until a time point when a phase between the current crank angle sensor and a cam angle sensor detecting position of high-pressure fuel pump driving cam is decided. Thereby, it is possible to shorten the engine start time period, reduce emission gas substances and increase the engine output, for example, as shown in Japanese laid-open patent publication 2005-23942.
A high-pressure fuel pump having a normal close type solenoid valve realizes full discharge with good pressure rising responsibility by non-power energization, however there is a possibility to energize continuously during long time in the case depending on the engine operation mode. For example, in the state which no fuel is used such as engine braking, the solenoid valve is energized continuously to maintain in valve opening state during the full period of pump compression stroke so as not to discharge continuously fuel by the high-pressure pump. As a result, it causes problems such as over heat of the solenoid valve and increase of energy consumption of the entire system and the driving circuit load.
Additionally, in the power energization control to the solenoid valve, unless appropriate start and finish of the power energization are performed, unintentional increase and decrease of pressure are caused in the pressure accumulating chamber (hereinafter referred to as common rail), and the pressure of the high-pressure fuel supplied to the fuel injector does not reaches a target fuel pressure to realize the most suitable combustion and results in the deterioration of combustion stability and emission gas property.